Mixing and kneading device for polymer compositions

ABSTRACT

A mixing/kneading device ( 10 ) for receiving a viscous composition and for admixing at least one additional constituent therewith, said device comprising: an elongated cavity ( 11 ) formed by an enclosure ( 15 ) and having a length and a diameter, and including a first inlet ( 112 ) for introducing said viscous composition into said device, and at least one second inlet ( 111 ) for introducing said at least one 10 additional constituent; and an outlet end ( 119 ) downstream of said first and said second inlet for connecting said mixing/kneading device with a processor; a pair of elongated rotors ( 12,14 ) for co-rotation within said cavity ( 11 ); said elongated rotors each having a first and mutually inter-matching flight portion ( 121;141 ) closely fitting into said cavity ( 11 ) and being adapted to forcingly convey said viscous composition and said at least one additive distributed therein through said cavity ( 11 ) towards said outlet end ( 119 ) thereof; and at least one non-conveying portion ( 161;182 ) downstream of each of said first portions ( 121;141 ) adapted to improve said distribution of said at least one additive in said viscous composition.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to processing of viscouscompositions, preferably but not exclusively to plasticated polymercompositions, such as normally solid thermoplastic polymers at extrusiontemperatures of typically in the range of from about 150-300° C.

A problem connected with such processing is uniform admixing of varioustypes of additional components or additives with such polymercompositions. Generally, such admixing is effected when the polymercomposition is in a plasticated or molten state. However, because of thegenerally high viscosities of polymer compositions at processingtemperatures this is not without problems because fillers, such as glassfillers or fibers, which—while sometimes effective to mechanicallyreinforce the resulting products—are relatively fragile and tend tobecome comminuted or excessively disaggregated or disintegrated whenexposed to forces generated upon mixing so that their maximumcontribution to the quality of the final product produced is notattained.

2. Prior Art

Various means and methods for effective admixing additives includingfillers with polymer compositions are known in the art. In fact, manyprocessors of the screw, extruder type are used for this purpose buttend to comminute fragile fillers. Special mention deserve co-rotatingtwin screw extruders which are widely used for compounding thermoplasticpolymers. Such devices have been developed over the past decades withincreasing processing velocities, e.g. up to 1200 RPM, to satisfyhighest throughput requirements. It may happen, however, that such highspeed may conflict seriously with the desired quality for severalapplications, e.g. when a low or a very low processing speed is requiredto achieve a given quality. It would not be helpful, however, to useconventional plasticating mixers, such as co-rotating twin screwextruders, and to simply reduce the processing speed because at low orvery low speeds melting conditions cannot be achieved. As known to thoseskilled in extrusion art, melting of polymers often needs a certainamount of frictional heat developed by the screws upon rotation;however, when operation speed is under a certain critical threshold, notenough frictional heat will be generated by the rotating screws, and notenough thermal energy for melting will be provided by the extrusionsystem. In other words, when using a conventional screw extruder wherethe same shaft effects both plastication and mixing, it will bedifficult, at best, to simultaneously achieve an optimum speed forplastication as well as an optimum speed for mixing; this is due to thesimple reason that such two optimal speeds will differ. However, aparticular processor type termed “port device” for adding variousconstituents to viscous polymer compositions within an extruder isdisclosed in EP-A-0 907 492 as well as in the references discussedtherein, and EP-A-Q 907 492 is incorporated herein for the purpose ofdisclosure and delimitation.

OBJECTS AND BRIEF DEFINITION OF THE INVENTION

The problem of optimally admixing additional constituents to a polymercomposition and, notably strain rate control of mixing systems, has notbeen solved in a satisfactory manner by the means and methods providedby the art.

Research leading to the present invention has indicated that effectivecontrol of both distributive effects as well as of dispersing effects ofnixing devices and operations is needed for optimal product quality inthe general sense that distributive effects are maintained strong whiledispersing effects may be controlled between near zero and a maximumvalue, depending upon the nature of the processed system. In otherwords, what is required is a strain controlled mixing system also termedSCM herein below, where strain is defined as the product of the shearrate and the shearing time.

Accordingly, it is a general object of the present invention to overcomethe limitations of prior art mixing means and methods and to providestrain controlled mixing. It has been found according to the inventionthat this aim can be achieved with an improved port device capable ofproviding such optimum control of mixing conditions for precludingundesired effects with regard to the properties of the addedconstituents as well as with regard to the quality of distribution ofthe added constituent an apparatus as defined in claim 1. Preferredapparatus embodiments have the features specified in claims 2-9.

Further, the invention provides for a method of strain-controlled mixingof a viscous fluid with a filler or pigment as specified in claim 10.

Preferred method embodiments are as specified in claims 11 and 12 whileclaims 13-15 specify a shaped article obtained by the method of claim10.

EP 1 002 633 describes au apparatus in which a first and upstreamprocessor is used to produce a stream of a molten/plastifiedthermoplastic resin which is fed into a second and downstream processor.This second processor is a co-rotating twin screw extruder havingconveying portions as well as non-conveying portions arranged downstreamof the conveying portions and is used as a port device for introducing aher constituent into the stream of molten thermoplastic resin producedin the upstream processor. However, since the constituent added isrubber which is kneaded and molten in the port device there is noseparation of melting and admixing. Accordingly, strain controlledmixing cannot be achieved because the energy input into the port devicemust be sufficient to achieve both melting of the added constituent aswell as mixing the resulting melt with the molten thermoplastic resinfed into e port device.

in the polymer composition. Further objects are improved straincontrolled processing means, methods and improved products obtained bystrain-controlled mixing.

These objects and further advantages as disclosed below will be achievedaccording to a first embodiment of the invention by a port device forreceiving a viscous composition, typically but not exclusively aplasticated polymer composition, and for admixing at least oneadditional constituent therewith which may be a filler or any other typeof addition conventionally used in the processing art; the port deviceaccording to the invention comprises an elongated cavity formed by anenclosure and having a length and a diameter, and including a firstinlet for introducing the viscous composition into the port; and atleast one second inlet for introducing the at least one additionalconstituent; and an outlet end downstream of the first and said secondinlet for connecting the port device with a processor; a pair ofelongated rotors for co-rotation within the cavity; the elongated rotorseach having a first and mutually inter-matching flight portion closelyfitting into the cavity and being adapted to forcingly convey theviscous composition and the at least one additive distributed thereinthrough the cavity towards the outlet end thereof; and at least onenon-conveying portion downstream of each of the first portions adaptedto improve the distribution of the at least one additive in the viscouscomposition.

According to a second embodiment, the present invention provides astrain controlled mixing system including a port device as disclosed thein herein operative connection with an upstream processor and adownstream processor.

Definitions and Preferred Embodiments of the Invention

Co-rotating rotors according to the invention having mutuallyintermatching flight portions fitting into the cavity are well known inthe art and are commercially available, typically in the form ofelements for assembly on an elongated core with suitable recesses orprotrusion and corresponding protrusions and recesses at the inside ofthe external elements of the rotors. Such elements may be of theconveying type (flights of various pitch angles) or non-conveying orkneading type. Whether or not an element of the conveying type is, infact, conveying, depends upon the pitch angle which may be “positive” or“negative” in relation to the axis of rotation. In this context, theexpressions “positive pitch angle” and “negative pitch angle” will beused herein as synonymous with “positive pitch” and “negative pitch”,respectively. Generally, a positive pitch will cause flow of materialtowards the outlet (“downstream direction”) while a negative pitch willcause flow of material towards the inlet (“upstream direction”).

Finally, the term “kneading elements” is used herein to refer toelements that may have the shape of conveying elements but with a helixangle is 90° so a to cause no flow in either direction. Conveyingelements may have different pitch, and both conveying and kneadingelements may have different length. The length or thickness of thekneading elements typically range between a few to a severalmillimeters, for example from 2 mm to 100 mm, depending on the requireddispersing rate of mixing.

The terms “upstream” and “downstream” are intended herein to refer tothe direction of flow of a viscous composition that is processed bymeans and methods according to the invention. For example, a processor(e.g. a plasticating extruder) that produces the feed or input for theport device is regarded as “upstream” with relation to the port devicewhile a processor (e.g. a production extruder) receiving the viscousmaterial plus admixed constituents from the port device will be regardedas “downstream”. In that context, an extruder can be said to be a“screw-type processor” because of the generally helical configuration ofthe rotors. Processors that include two inter-matching rotors may betermed “twin screw processors” and can be operated in counter rotationor co-rotation as is well known in the art.

However, the term “processor” as used herein is by no means restrictedto processors of the extruder type but is intended to include, interalia, output or shaping devices for directly transforming the outputmaterial from the port device into a product, e.g. into a continuous ordiscontinuous extrudate, e.g. a granulate or another type of amasterbatch material. Further examples of downstream processors in anapparatus or plant according to the invention are output controldevices, such as gear-operated melt pumps or screw flow valves.

Typically, rotors of twin-screw processors used for co-rotatingoperation have the same structures and dimensions but this is not acritical requirement per se but is preferred for practical reasons, suchas economy and simplicity.

The terms “cavity” and “enclosure” relate to what is also called a“barrel”, i.e. the outer member or housing of a screw-type processor.Again, matching barrels are obtainable commercially from variousproducers. Such housings may be provided and used with various types oftemperature control devices, such as cooling means, and heaters.

According to a preferred embodiment, the first conveying flight portionof each of the rotors is formed by a first helical scraping flightportion having a positive pitch while the second non-conveying sectionof each of the intermeshing rotors is formed by a kneading elementsection or by a second helical scraping flight section having a negativepitch.

The terms “ad mixing”, “mixing” and “mixtures” are used synonymouslyherein with such terms as “interblending”, “blending”, and “blend” andare intended to refer to any process that reduces non-uniformity of acomposition that is formed of two or more constituents. This is animportant step in polymer processing because mechanical, physical andchemical properties as well as product appearance generally aredependent upon the uniformity of the composition of a product. Typicalexamples of “mixing” as used herein involve both solid/liquid,liquid/liquid and gas/liquid systems, such as blending polymercompositions with color concentrates, fillers, gas, or other additives.Accordingly, “mixture” as result of a mixing step is defined herein asthe state formed by a composition of two or more ingredients which maybut need not bear a fixed proportion to one another and which, howevercommingled, may but need not be conceived as retaining a separateexistence. Generally, a mixing step according to the invention is anoperation which is intended to reduce non-uniformity of a mixture.

Dispersion of carbon black or organic pigments, agglomerates or clustersin a viscous melt, e.g. of a polyalkene, such as polyethylene andpolypropylene, is a typical and important example of a solid/liquidmixing operation according to the invention while blending of polymermelts is an example of liquid/liquid distributing operation according tothe invention. Further, mixing a gaseous component, e.g. nitrogen, intoan LDPE polymer viscous matrix to achieve foamed products is anotherexample of gas/liquid mixing operation, according to the invention. Suchoperations are dominated by one overriding factor: the viscosity of suchsystems.

From this context it is apparent that compositions with very highviscosities, say in the range of up to 10,000 Pas or above are regardedas “liquid” for the purposes of the invention provided that suchcompositions are capable of being processed in extruder-type processingmeans which include suitable temperature control to maintainprocessability of a given composition. Further, while polymercompositions are preferred examples for use according to the invention,other types of viscous compositions of matter, such as sludges and tars,are considered for processing in a port device according to theinvention.

The term “polymer composition” as used herein is intended to includeboth synthetic as well as natural and semi-synthetic polymers. The term“polymer” is used synonymously with “macromolecular substances” andincludes any type of polymer, such as homopolymers, copolymers, graftpolymers and any mixtures thereof including mixtures with substancesthat are not polymeric but monomeric or oligomeric, such as varioustypes of plasticizers, fillers, stabilizers, and other additives used inprocessing. The term “plasticating” or “plastification” refers totransformation of a normally solid material into a “softened”, “molten”or other viscous state. Typically, this is achieved by heating a polymercomposition to a temperature where the composition becomes capable offlow.

In practice, the task of mixing an additional constituent with a viscouscomposition may range from an almost “pure distributive mixing” to acombination of “distributive-dispersing mixing”. The term “distributivemixing” is used hereto indicate a mixing operation which promotesoptimum spatial rearrangement of components so as to minimizenon-uniformity of the composition while the term “dispersive mixing” isused here to indicates that type of mixing where a minimum mechanicalenergy amount has to be introduced in the mixing step for achieving therequired mixing quality. For example, in a typical “soft mixing” casewhere hollow glass spheres are to be distributed in a polymer melt, themain problem to be solved is optimal distribution of such glass spheresin the polymer without affecting the integrity of the glass sphereswhich may be so brittle that mixing stress must be minimized.

Another example of the need to minimize mixing stress (mainly a shearstress) is required when mixing chopped glass strands with polymermelts. Strand filaments are often supplied in small bundles of thousandsof chopped glass fibers held together by such additives as silanesnormally used as sizing agents etc. For example, bundles of choppedfilaments of glass type “E” with a typical average length of 3-4,5 mm or8-15 mm are commercially sold by major glass fiber manufacturers, andsuch chopped glass bundles must be subjected to a very small amount ofshear stress during mixing so as to avoid glass fiber breakage.

Yet another typical case where a combination of a sufficientdistributive effect is required in combination with a very highdispersing action is mixing organic pigments, e.g. phtalocyanine blue,with a polymer composition, e.g. molten LDPE, for producing amasterbatch or pigment concentrate. In this case, it is desirable tobreak up pigment clusters into individual pigment particles in themicrometer range. Optimal dispersion of the particles yields a highercolor strength of the masterbatch and is essential for preventingpigment specks in the final products.

For many practical purposes, distributive effects should be high, ingeneral, while dispersing effects require fine tuning between near zeroand maximum. It should be noted in this context that in most continuousmixing devices for viscous polymer compositions, such as polymer melts,the flow mechanism is one of “drag flow” rather than positivedisplacement flow, or a shear flow mechanism because the flow is inducedby shearing the liquid and not by displacing it. This concept isimportant because the basic law governing such flows is the well-knownNewton Law of Viscosity. Further, shear flow happens to be a flowmechanism obtained in co-rotating twin screw extruders.

A strain controlled mixing (SCM) system provided by the invention isapplicable to all types of blending of polymers, polymer alloys,addition of filling and reinforcing polymers, production of high qualitymasterbatches with very high pigment concentrations and other processeswhere prior art does not provide for optimal solutions. An essential andnovel aspect SCM is the feature that the mixing processes may becontrolled to provide anything from a very soft to a very harddispersing rate of mixing as required by the particular use, either forproducing finished articles, semi-finished products, or pre-productssuch as pellets or masterbatches. In contrast to the art whereplastication and mixing steps are normally performed by the sameextruder which first melts the polymer and provides mixing downstream ofplastication, an SCM system according to the invention is based uponseparating the plastication stage from the mixing stage by using anupstream processor for generating the plasticated composition that isfed to a port device according to the invention for admixture withfurther constituents of the intended product.

A typical viscous composition of interest for the invention willpreferably have a viscosity in the range of from about 50 to about10.000 Pas for shear rates ranging between about 1 and about 1000 s⁻¹.In this context and with reference to any numeric value cited herein,the term “about” preceding such numerals generally is intended toinclude reasonable, positive or negative, variations of up to 30% of thegiven value.

Because of the dependence of viscosity from temperature and generalprocessing requirements, processing temperatures in a port deviceaccording to the invention will preferably be selected in the rangebetween the melting, or softening point, on the one hand and thetemperature of thermal decomposition, at the other. For practicalpurposes, a preferred range of operating temperatures is between about140° C. and about 320° C. for most thermoplastic polymers. It is to beemphasized, however, that application of the invention is not limited tothermally plasticated polymer compositions but is of use for processingof compositions that exhibit viscosity values in the above range atnormal room temperature (25° C.).

Another important concept connected with mixing is shear strain, i.e.the strain experienced by a fluid sheared for a certain time. Shearstrain units may be defined as the product of the shear rate in units ofs' and the mixing time in seconds thus yielding a unit without adimension. One and the same shear strain value may be composed of a widevariety of different shear rates and times. For example, 100 strainunits may be composed either of a shear rate of 20 s⁻¹ and a time of 5s, or vice versa, or by one of the infinite number of pair that yield aresult of 100 upon multiplication. Of course, not all such straincombinations have the same mixing value. While it is intuitive that therole played by the time is similar for both distributive and dispersingmixing as it relates to the number of passages experienced by the meltcomposition through the mixing zones of interest, yet a proper shearrate may be a critical issue, mainly in the case of dispersive mixing.Since insufficient mixing time or insufficient shear rate may lead to anunacceptably low product quality—while an excessive time or shear ratemy lead to polymer degradation and/or excessive processing costs—bothmixing time and shear rate can be determined with very simple means bythe operator on a case-by-case basis, in order to achieve an optimumresult of a specific mixing task. This type of special control of mixingtime and shear rate (mixer's speed) is what is referred to herein as astrain controlled mixing system (SCM).

An important property of a port device according to the invention is itsinherent ability to provide an adjustable shearing rate by adjusting thespeed of rotation when operating a port device according to theinvention. Thus, typical speeds of rotation of the rotors in a portdevice according to the invention will be in the range from about 5 toabout 600 rotations per minute (RPM) and preferably in the range of fromabout 5 to 300 rotations per minute (RPM).

Mixing times in a port device according to the invention will bedependent upon the geometry of the port device and the flow rate of theviscous composition that is fed to the port device. For that reason, thequality or geometry of an upstream device, e.g. a plasticating extruder,that produces the viscous composition may be a useful parameter in anapparatus according to a second general embodiment of the inventionincluding a port device as a component in addition to an upstreamprocessor for generating the viscous composition and a downstreamprocessor for receiving the admixture produced by the port device andfeeding it into a shaping step for obtaining a shaped product.

Thus, according to a preferred embodiment of the invention, the portdevice will have a relatively short axial length and a relatively widescrew diameter. Typically, a preferred port device and a preferred ratiobetween the length of the elongated cavity length and the diameter ofthe cavity (also termed L/D ratio) will be in the range of about 2 toabout 20.

In that context, the ratio of the external diameter of the screw to thescrew core diameter, also termed D/d ratio, (where the screw core equalsto the external screw diameter reduced by twice the channel depth) willpreferably be relatively high so as to allow for the largest mixingvolume available with given overall dimensions of the port device. Inpractice the upper critical limit for such D/d ratio is given by thetorque applicable on the rotor shafts and should be sufficiently high toproduce rotor's torsion or deformation according to the well known lawsof solid mechanics. It should be noted that for any given throughput apreferred port device according to the invention will be characterizedby a torque which is rather small when compared with the torqueapplicable with conventional co-rotating twin screw extruder. This isdue to the fact that in conventional devices both melting and maximummixing must be effected while only mixing occurs in a port device. Thisresults in a large ratio of the torque applied in a conventionalco-rotating twin screw extruder while the torque applicable in a portdevice typically is in the order ranging from about 2 to about 4.

As a consequence of the aspects just mentioned, the D/d ratio in a portdevice according to the invention will be preferably in the range offrom about 1,3 to about 3 and more preferably between about 1,4 and 2,5.

Again, with reference to an apparatus including a port device positionedbetween an upstream device for generating a viscous composition that isfed to a port device which, in turn feeds a downstream processor forproducing a shaped article, it is preferred that the upstream processoralso is a co-rotating twin screw extruder of the high speed type, e.g.capable of operating at speeds of up to 1200 RPM, and dedicated, inessence, to melt or plasticize the polymer to be fed into the portdevice; this provides an excellent melting rate in the most compactspace for maximum process economy when using, for example, smalldiameter and high speed extruders. As an example, it has been found inthe practice of the invention that an upstream co-rotating twin screwextruder of 40 mm diameter and a length of 10-15 diameters used toproduce the feed for a port device according to the invention istypically capable of plasticating up to 0,3-0,4 kg per hour per rotationof typical polyolefins so as to yield an output of about 360 kg per hourto 480 kg per hour at 1200 RPM.

The port device according to the invention arranged downstream of theplasticating co-rotating twin screw processor should be designed for acorresponding input (e.g. 400 kg per hour) while having a diameter thatis about 1 to about 5 times greater than the diameter of the upstreamprocessor (e.g. 120 mm diameter) and a total length ranging from about 5to about 15 times the diameter, depending upon the application.

Another ratio of interest in this connection is the ratio of the speedof rotation of the upstream processor (producing the feed for the portdevice) to the speed of rotation of the rotors of the port device.Preferably, such ratio will be in the range of from about 2 to about 15.

A port device according to the invention can be operated in variouspositions from horizontal to vertical as long as gravity does notsignificantly affect conveying action of the rotors. According to anembodiment preferred for many purposes, the cavity and the rotors of aport device extend in an essentially vertical direction in the sensethat material flow through the port will be downward so that gravitationcontributes rather than opposes the conveying action of the first flightportions. Vertical design may provide important benefits, such ascompact arrange-ment, an advantageous filling rate independently fromthe rotor's speed, a most effective venting of the melt upstream of themixing zone and other benefits of vertical orientation.

As mentioned briefly above, a second general embodiment of the inventionis an apparatus or “plant” for processing a stream of a viscous polymercomposition to produce an extrudate formed by the polymer composition;such apparatus comprising:

-   -   at least one port device as disclosed herein;    -   at least one processor, e.g. a plasticating extruder and        preferably a co-rotating twin screw extruder, arranged in        operative upstream connection with the port device (i.e. for        generating the plasticated polymer composition that is fed into        the port device and generally termed “upstream processor”        herein); and    -   at least one processor, e.g. a production extruder, connected to        a shaping means, e.g. as a calender, extrusion die, spinneret,        injection mold, press mold, etc., arranged in operative        downstream connection (termed “downstream processor” herein)        with the port device.

Preferably, the upstream processor is a co-rotating intermeshingself-wiping extruder having a cavity with a diameter such that a ratioof the diameter to the diameter of the elongated cavity of the portdevice is in the range of from about 1:1 and 1:5.

According to a further general embodiment the invention provides for amethod of producing shaped articles made of a polymer compositioncontaining at least one normally solid filler; the method includesproviding an apparatus as defined above and shaping the viscous polymercomposition containing the filler for obtaining the articles. While anytype of filler used in the art is suitable for processing according tothe invention, a preferred filler is a particulate filler formed of arelatively brittle material such as mineral glass in the form of glassfibers having an average length of at least about 2 mm, hollow glassspheres, etc.

Consequently, the invention provides shaped articles obtained by themethod disclosed herein, for example in the shape of load-bearing panelscomprising a polymer composition and a reinforcing filler for achievinga flexural modulus of at least 6000 MPa (10 ⁶ Pascal), preferablyprovided with a scratch-resistant and slip-resistant surface.

Finally, the invention provides a method of processing polymercompositions by distributing a reinforcing filler therein comprising thesteps of providing a plasticated polymer composition; introducing theplasticated polymer composition into a port device as disclosed herein;adding a reinforcing filler to the plasticated polymer composition inthe port device; distributing the reinforcing filler without significantcomminution thereof in the plasticated polymer composition by operatingthe elongated rotors; and discharging the plasticated composition withthe reinforcing filler distributed therein.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be disclosed in more detail with reference to theenclosed drawings representing various non-limiting examples of variousembodiments of the invention. In the drawings:

FIG. 1 is a diagrammatic sectional view of an embodiment of a portdevice according to the invention;

FIGS. 1A and 1B are diagrammatic sectional views of the non-conveyingportion of the rotors of a port device as shown in FIG. 1;

FIGS. 1C and 1D are sectional views to illustrate configuration of therotors shown in FIG. 1;

FIG. 2 is a diagrammatic side view, partially sectioned, of amulti-component apparatus or plant according to the invention;

FIGS. 2A, 2B and 2C are diagrammatic side views of various shaping toolsat the outlet end of the downstream production extruder shown in FIG. 2;

FIG. 3 is a diagrammatic side view of another shaping tool forconnection with the outlet end of the downstream production extruder ofFIG. 2;

FIG. 4 is a diagrammatic side view of yet another shaping tool forconnection with the outlet end of the downstream production extruder ofFIG. 2;

FIGS. 5 and 6 are perspective views of preferred products obtainedaccording to the process of the invention; and

FIG. 7 is a diagrammatic top view, partially sectioned, of amulti-component apparatus or plant according to the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The port device 10 shown in FIG. 1 is illustrated in a diagrammatic andpartially sectioned view and comprises a cavity 11 which is the interiorspace of an enclosure 15 in the form of a housing or barrel forreceiving a pair of elongated rotors 12,14 connected at their upper end17 to a drive (not shown in FIG. 1) and having a first or upper andconveying section 121,141 and a lower or second non-conveying section161,182 explained below in more detail with reference to in FIGS. 1A and1B.

A first inlet 112 near the upper end of enclosure 15 serves as aconnection for introducing a plasticated polymer or other type ofviscous composition delivered by an upstream device (not shown in FIG.1). A second inlet 111 serves to introduce an additional constituentwhich may be a liquid or a particulate solid material, typically afiller, delivered, e.g. by a hopper with or without a metering device(not shown in FIG. 1). Outlet 119 is arranged at the lower end of portdevice 10 for connection with a downstream processor (not shown in FIG.1).

The non-conveying sections 161,182 of the rotors 12,14 may be formed bya pair of inter-matching kneading sections 161 a, 182 a as illustratedin FIG. 1A or by a pair of inter-matching flight portions 161 b, 182 bwith reversed or negative pitch as illustrated in FIG. 1B.

FIG. 1C illustrates various dimensions, namely the distance “a” betweenthe axes of rotors 12,14; maximum width “D” of the flight sections;minimum width “d” of the flight sections; and the width “h” of theoverlap area.

An apparatus or plant 20 representing a strain-controlled mixing systemaccording to the invention is shown diagrammatically in FIG. 2 andcomprises a port device 210 as described above formed by a pair ofrotors 21 a, 21 b in an enclosure in the manner disclosed in FIG. 1.Port device 210 is provided with an optional re-circulating conduit 29indicated in broken lines and including conventional flow control means(not shown) for regulating the degree of re-circulation, if any.

Plasticated feed composition is produced in upstream processor 201,preferably an extruder fed by a conventional metering device 202 andbeing in operative connection with port device 210 via inlet 211. Afiller, e.g. a reinforcing or non-reinforcing filler and/or a pigment,or another constituent of the product to be processed by downstreamprocessor 203 is added by a second upstream conveyor 212 fed by anotherconventional metering device 213.

Port device 210 includes a drive 28 and is in operative connection withdownstream processor 203, e.g. a conventional production processor. Theoutlet end 204 thereof may be connected to any output device, e.g. acombination 206 of a slit die plus calender as shown in FIG. 2A, aspin-die manifold or spinneret 207 as shown in FIG. 2B, a shaping die208 as shown in FIG. 2C or another type of product-shaping device knownin the art of polymer processing.

Another type of a process output device for connection with the outputend 204 of downstream extruder 203 of FIG. 2 is shown diagrammaticallyin FIG. 3. Device 30 receives the completely compounded plasticatedpolymer composition produced in port device 210 via downstream extruder203 by means of connector 304 and includes an injection press formed bybarrel 32 and a reciprocating ram or piston 31 for injection into amolding machine 37 formed between two press plates 34,36 and aconventional mold 39. Drive means for operating ram 31 and moldingmachine 37 are needed, of course, for operation but are omitted in FIG.3 for reasons of simplicity.

A similar process output device 40 is shown diagrammatically in FIG. 4where, again, the output material from downstream processor 203 of FIG.2 is fed via connector 404 into an injection press of similarconstruction as shown in FIG. 3, i.e. with a barrel 42 and areciprocating ram or piston 41 arranged therein. The viscous compositionis introduced into a molding press 47 formed by an upper die 46 and alower die 49 between platens 44, 45 which are operated in areciprocating fashion by a drive (not shown).

FIG. 5 and FIG. 6 are perspective views of a fiber-reinforcedload-bearing panel 50 and 60, respectively, formed of a polymercomposition, e.g. on the basis of recycled polypropylene and containinga reinforcing filler, e.g. glass fibers of the type mentioned above.Panels 50,60 are formed by a shell 51, 61 that encloses four parallellongitudinal tunnels 52,62. Panels of this type are known per se, e.g.from WO 00/31356 incorporated herein for further details. Very highstrength parameters can be achieved, e.g. a flexural modulus of at least6000 MPa. Preferably and according to the present invention, the topfaces are made wear-resistant by inclusion of small solid glass spheresin the polymer composition used for the top coating of both as well asslip-resistant by embossing the top face 53 in a dome-shaped fashion ortop face 63 in a cross-ribbing fashion.

As will be apparent from the above explanation of the SCM systemaccording to the invention, improved admixing of reinforcing filleraccording to the present invention provides for improved product qualityand/or economy.

FIG. 7 shows a further embodiment of an apparatus 70 for straincontrolled mixing, e.g. in the production of masterbatch materials orpigment concentrates. The upstream processor 701, preferably aplasticating extruder fed by a conventional metering device 702 is in anoperative connection with port device 710 via inlet 711. A meteringdevice 71 is used to introduce a liquid or solid constituent, e.g. astabilizer, pigment or other conventional component for polymerprocessing into port 710. It should be noticed that in the case ofintroducing a gas, such as nitrogen, for mixing into a polymeric viscouscomposition in the port device, such gas should be fed by a conventionalgas nozzle in a position of the elongated cavity (11) which is close tothe non-conveying zone (161,182) in order to avoid gas escape as it iswell know to the skilled persons in the art of producing products basedon foamed polymeric compositions. Drive and gear means 77,72 areprovided for operation of port device 710, the output of which is fedinto a conventional strand die group 703 for further pelletizing.

EXAMPLES Example 1

Recycled polypropylene was plasticated in the upstream processor (screwdiameter 45 mm, length 25 D) of an apparatus as shown in FIG. 2 andintroduced into the port device (a co-rotating, fully intermeshingself-wiping twin screw; screw diameter 60 mm, length 10D and anon-conveying end portion as shown in 1B) as a plasticated polymercomposition under operating conditions for plastication. Chopped glassfibers with an initial length of about 8 to 10 mm were added by ametering device so as to make up about 30% by weight of the finalcomposition that is passed from the port device to the downstreamprocessor and from there into an extrusion head and, further downstream,into a calibration section for producing structural panels having arigidity of above 7,000 MPa.

Example 2

Commercial linear low density polyethylene (LLDPE) was plasticated inthe upstream processor of an apparatus as shown in FIG. 2 and asspecified in Example 1 and introduced into the port device(non-conveying end portion as shown in FIG. 1A) as a plasticized polymercomposition. Micronized calcium carbonate was added by a metering deviceso as to make up about 50% by weight of the final composition that ispassed from the port device to the downstream processor equipped forproducing high filled stretchable film.

The product film obtained had a very good appearance and was capable ofpassing water vapor after stretching (up to about 3.5 times its lengthin unstretched state).

Example 3

A series of tests were made with a port device as shown in FIG. 1 havinga D/d ratio (ratio of inner barrel diameter to the same value reduced bytwice screw depth) of 1.72 and a vertical arrangement. Different polymermelt compositions were processed at various speeds, residence times andmixing volumes according to the specific task to be achieved. Theresults are displayed in Table 1. TABLE 1 (Screw diameter 60 mm) FillingAv. Mixing rate in Shear axial Mixing the Volumetric Mixing Mixer Av.Shear Strain Comp Case length Volume mixing flow rate Throughput Timespeed Rate (Strain arative No. (m) (m³) section (m³/s) (kg/hr) (s) (rpm)(s⁻¹) Units)* strain 1 0.10 0.00018 1 0.0000029 10 62 10  2,5 155  1 20.15 0.00027 1 0.0000029 10 94 10  2,5 235  1,51 3 0.20 0.00036 10.0000029 10 124 10  2,5 310  2 4 0.10 0.00018 1 0.0000029 10 62 20  5310  2 5 0.10 0.00018 1 0.0000029 10 62 30  7,5 465  3 6 0.10 0.00018 10.00001462 50 12 30  7,5 90  0,58 7 0.10 0.00036 1 0.0000029 10 124 20050 6200 40*The actual shear rate was calculated for a screw channel depth of 12,5mm and the comparative shear strain was calculated by dividing allvalues for the case 1 value.

While various embodiments have been disclosed and illustrated above insome detail it is to be emphasised that such detailed disclosure relatesto non-limiting examples so that various modifications and changes willbe obvious. For example, while temperature and pressure conditions ofoperation have not been explained in detail, it will be apparent thatviscosity is a temperature-dependent parameter but that operatingtemperatures must not cause decomposition. Further, it is well knownthat operation of screw-type processors tends to generate heat, due tothe viscous heat dissipation which occurs parallel to mixing, so thatcooling and/or heating means may be required for optimum operation ofthe invention. Various other operating parameters are known to be ofpractical importance for commercial operation and have not discussedherein for reasons of brevity. Thus, the scope of the invention is to bedetermined by construeing the subsequent claims with the knowledge ofthose experienced in the art of polymer processing.

1. An apparatus for admixing a viscous composition with at least oneadditional constituent selected from fillers, fibers, pigments, colorconcentrates and gases; said apparatus comprising an upstreamplasticating extruder (201, 701) for producing a stream of a viscous;polymer composition and a downstream processor for receiving said streamand for introducing said additional constituent, said downstreamprocessor being a port device (10) for receiving said viscouscomposition from said upstream plasticating extruder and for admixingsaid at least one additional constituent therewith, said port devicecomprising: an elongated cavity (11) formed by an enclosure (15) andhaving a length and a diameter (D), and including a first inlet (112)for introducing said viscous composition into said port; and at leastone second inlet (111) for introducing said at least one additionalconstituent; and an outlet end (119) downstream of said first and saidsecond inlet for connecting said port device with a processor; a pair ofelongated rotors (12, 14) for co-rotation within said cavity (11); saidelongated rotors each having a first and mutually inter-matching flightportion (121; 141) closely fitting into said cavity (11) and beingadapted to forcingly convey said viscous composition and said at leastone additional constituent distributed therein through said cavity (11)towards said outlet end (119) thereof, and at least one non-conveyingportion (161; 182) downstream of each of said first portions (121; 141)adapted to improve said distribution of said at least one additionalconstituent in said viscous composition; wherein said diameter (D) ofsaid cavity (11) is about 1 to 5 times greater than the diameter of theupstream plasticating extruder, and wherein said cavity has a length:diameter ratio in the range of from about 2 to about
 20. 2. Theapparatus of claim 1, wherein said first conveying flight portion (121;141) of each of said rotors (12; 14) is formed by a first helicalscraping flight portion having a positive pitch.
 3. The apparatus ofclaim 1, wherein said non-conveying portion (161; 182) of each of saidintermeshing rotors (12; 14) is formed by a kneading element section(161 a; 182 a).
 4. The apparatus of claim 1, wherein said non-conveyingflight portion (161; 182) of each of said intermeshing rotors (12; 14)is formed by a second helical scraping flight section (161 b; 182 b)having a negative pitch.
 5. The apparatus of claim 1, wherein saidelongated cavity (11) formed by said enclosure (15) extends in anessentially vertical direction.
 6. The apparatus of claim 1 forprocessing said stream of said viscous composition to produce anextrudate formed by said viscous composition and a filler, fiber ofpigment admixed therewith, said apparatus additionally comprising: atleast one processor (203; 703) arranged in operative downstreamconnection with said port device for producing a shaped product.
 7. Theapparatus of claim 6, wherein said at least one processor (203; 30; 40;703) arranged in operative downstream connection with said port devicehas an output means (206; 207; 208; 37; 47; 703) for shaping saidviscous composition emanating from said port device.
 8. The apparatus ofclaim 6, wherein said plasticating extruder (201; 701) arranged in saidupstream connection with said port device is a co-rotating intermeshingself-wiping extruder.
 9. A method for strain-controlled mixing of aviscous composition with at least one additional constituent selectedfrom fillers, fibers, pigments, color concentrates and gases, saidmethod comprising the steps of producing a stream of a viscous polymercomposition in a plasticating extruder (201; 701) and feeding saidstream into a downstream processor for admixture with said at least oneadditional constituent; wherein said downstream processor is a portdevice (10) for receiving said viscous composition from saidplasticating extruder, said port device comprising: an elongated cavity(11) formed by an enclosure (15) and having a length and a diameter (D),and including a first inlet (112) for introducing said viscouscomposition into said port; and at least one second inlet (111) forintroducing said at least one additional constituent; and an outlet end(119) downstream of said first and said second inlet for connecting saidport device with a processor; a pair of elongated rotors (12; 14) forco-rotation within said cavity (11); said elongated rotors each having afirst and mutually inter-matching flight portion (121; 141) closelyfitting into said cavity (11) and being adapted to forcingly convey saidviscous composition and said at least one additional constituentdistributed therein through said cavity (11) towards said outlet end(119) thereof, and at least one non-conveying portion (161; 182)downstream of each of said first portions (121; 141) adapted to improvesaid distribution of said at least one additional constituent in saidviscous composition; and operating said port device for maximizingdistributive effects while maintaining dispersing effects between zeroand maximum.
 10. The method of claim 9 for producing shaped articlesmade of a polymer composition containing at least one filler; comprisingthe step of feeding the mixture obtained into a downstream processor(203; 30; 40; 703) for producing a shaped article from said mixture. 11.The method of claim 10, wherein said filler is a particulate reinforcingfiller, such as glass fibers having an average length of at least 2 mm.12. A shaped article obtained by the method of any of claims 10, whichis a load-bearing panel (50; 60) comprising polypropylene as saidpolymer composition and containing about 30% by weight of chopped glassfibers with an initial length of about 8-10 mm as said reinforcingfiller for obtaining a flexural modulus of at least 6000 MPa.
 13. Theshaped article of claim 12, wherein said load-bearing panel has awear-resistant and slip-resistant surface.
 14. A shaped article obtainedby the method of claim 10, which is a stretchable film comprising LLDPEand about 50% by weight of micronized calcium carbonate.
 15. Theapparatus of claim 2, wherein said non-conveying portion (161; 182) ofeach of said intermeshing rotors (12; 14) is formed by a kneadingelement section (161 a; 182 a).
 16. The apparatus of claim 2, whereinsaid non-conveying flight portion (161; 182) of each of saidintermeshing rotors (12; 14) is formed by a second helical scrapingflight section (161 b; 182 b) having a negative pitch.
 17. The apparatusof claim 2, wherein said elongated cavity (11) formed by said enclosure(15) extends in an essentially vertical direction.
 18. The apparatus ofclaim 3, wherein said elongated cavity (11) formed by said enclosure(15) extends in an essentially vertical direction.
 19. The apparatus ofclaim 4, wherein said elongated cavity (11) formed by said enclosure(15) extends in an essentially vertical direction.
 20. The apparatus ofclaim 2 for processing said stream of said viscous composition toproduce an extrudate formed by said viscous composition and a filler,fiber of pigment admixed therewith, said apparatus additionallycomprising: at least one processor (203; 703) arranged in operativedownstream connection with said port device for producing a shapedproduct.
 21. The apparatus of claim 3 for processing said stream of saidviscous composition to produce an extrudate formed by said viscouscomposition and a filler, fiber of pigment admixed therewith, saidapparatus additionally comprising: at least one processor (203; 703)arranged in operative downstream connection with said port device forproducing a shaped product.
 22. The apparatus of claim 4 for processingsaid stream of said viscous composition to produce an extrudate formedby said viscous composition and a filler, fiber of pigment admixedtherewith, said apparatus additionally comprising: at least oneprocessor (203; 703) arranged in operative downstream connection withsaid port device for producing a shaped product.
 23. The apparatus ofclaim 5 for processing said stream of said viscous composition toproduce an extrudate formed by said viscous composition and a filler,fiber of pigment admixed therewith, said apparatus additionallycomprising: at least one processor (203; 703) arranged in operativedownstream connection with said port device for producing a shapedproduct.
 24. The apparatus of claim 7, wherein said plasticatingextruder (201; 701) arranged in said upstream connection with said portdevice is a co-rotating intermeshing self-wiping extruder.
 25. A shapedarticle obtained by the method of claim 11, which is a load-bearingpanel (50; 60) comprising polypropylene as said polymer composition andcontaining about 30% by weight of chopped glass fibers with an initiallength of about 8-10 mm as said reinforcing filler for obtaining aflexural modulus of at least 6000 MPa.